<i>In Amnio</i> MRI of Mouse Embryos

<div><p>Mouse embryo imaging is conventionally carried out on <i>ex vivo</i> embryos excised from the amniotic sac, omitting vital structures and abnormalities external to the body. Here, we present an <i>in amnio</i> MR imaging methodology in which the mouse embryo is retained in the amniotic sac and demonstrate how important embryonic structures can be visualised in 3D with high spatial resolution (100 µm/px). To illustrate the utility of <i>in amnio</i> imaging, we subsequently apply the technique to examine abnormal mouse embryos with abdominal wall defects. Mouse embryos at E17.5 were imaged and compared, including three normal phenotype embryos, an abnormal embryo with a clear exomphalos defect, and one with a suspected gastroschisis phenotype. Embryos were excised from the mother ensuring the amnion remained intact and stereo microscopy was performed. Embryos were next embedded in agarose for 3D, high resolution MRI on a 9.4T scanner. Identification of the abnormal embryo phenotypes was not possible using stereo microscopy or conventional <i>ex vivo</i> MRI. Using <i>in amnio</i> MRI, we determined that the abnormal embryos had an exomphalos phenotype with varying severities. <i>In amnio</i> MRI is ideally suited to investigate the complex relationship between embryo and amnion, together with screening for other abnormalities located outside of the mouse embryo, providing a valuable complement to histology and existing imaging methods available to the phenotyping community.</p>